1. Field of the Invention
This invention relates to measurement systems. More particularly, the invention relates to systems and methods for measuring the weight and determining the characteristics of moving vehicles.
2. Description of Prior Art
There are several varieties of weigh-in-motion systems currently available for moving vehicles which use various types of mechanisms for weighing the moving vehicle. The most common of these weighing systems rely on piezoelectric sensors, hydraulic load cells, bending plate strain gauges, linear variable differential transformers, and capacitive mats. Hydraulic load cells and bending plate strain gauges are considered to be the most accurate of these mechanisms.
Dynamic weighing systems to date appear to rely on an "ideal" response of vehicle tires rolling over a linear sensor. Theoretically, all of the information required is available to determine a gross weight and center of balance. An "ideal" response for a very carefully designed level and smooth road bed is not achieved in more than three-fourths of the weighing situations due to vehicle oscillations as the tires roll over the sensor. These oscillations can be in any direction: Vertical, side-to-side, or front-to-back. To overcome these situations, the sensor must be larger than the tire footprint (or not all the tire will be weighed during a peak weight measuring method). If the vehicle happens to be rocking from side-to-side (a situation observed many times) as the vehicle traverses the sensors, then the sum of the left and right power peaks will produce an artificially high result.
Prior art related to weighing moving vehicles is as follows:
U.S. Pat. No. 4,049,069 issued Sep. 20, 1996, discloses apparatus for measuring the weight of a moving vehicle. The apparatus includes a series of platforms with the length of each platform being shorter than the distance between axles; means for converting displacement of the platforms to electrical signals and electronic means for averaging the signals produced by the individual axle loads to produce the weight of the moving vehicle.
U.S. Pat. No. 5,260,520 issued Nov. 9, 1993, and assigned to the same assignee of the present invention, discloses apparatus for weighing a vehicle in motion using a plurality of elongated fiber-optic sensors defined by an optical fiber embedded in a casement of elastomeric material and disposed parallel to each other on the roadway in the path of a moving vehicle. Switch means are used in conjunction with the sensors to provide signals indicative of the speed of the moving vehicle, the number of axles, weight distribution, tire position, and the wheel base of the vehicle. The switch means are formed of optical fibers and the extent of light transmission through the fibers during contact with the tire of the vehicle is indicative of the vehicle weight.
None of the prior art discloses a weigh-in-motion system and method for moving vehicles in which an "ideal" weigh-in response is achieved in spite of vehicle oscillation occurring as sensors are traversed by the vehicle.